Phytophthora infestans belongs to the group of fungi referred to as Oomycetes. Phytophthora infestans infects various members of Solanaceae, such as potato, tomato and some ornamentals. It causes late blight of potatoes and tomatoes affecting all parts except roots. Geographically, the fungus is widely distributed, and it can be found in all potato-producing countries. Economically late blight in potatoes is of major importance, as infection early in the season can severely reduce crop yield. Currently the disease is controlled by spraying chemical fungicides (dithiocarbamates, such as mancozeb, manec and zineb) regularly. (For a review, vide: European Handbook of Plant Diseases, ed. by I. M. Smith et al., 1988, Blackwell Scientific Publications, Ch.8). Both from an environmental and economical point of view, biological control of diseases caused by Phytophthora infestans could have advantages over the use of chemical fungicides. A protein with antifungal activity, isolated from TMV-induced tobacco leaves, which is capable of causing lysis of germinating spores and hyphal tips of Phytophthora infestans and which causes the hyphae to grow at a reduced rate, was disclosed in WO91/18984 A1. This protein has an apparent molecular weight of about 24 kDa and was named AP24. Comparison of its complete amino acid sequence, as deduced from the nucleic acid sequence of the AP24 gene, with proteins known from a database revealed that the protein was an osmotin-like protein.
Experiments are in progress to evaluate plants which relatively over-express AP24 for resistance against various other fungal pathogens.
Despite initial success in combating fungal pathogens, such as Phytophthora infestans, and the genetic engineering of plants capable of producing these antifungal proteins with activity against this fungal pathogen there remains a need to identify and isolate other proteins with antifungal activity against this fungus.